A denial-of-service attack (DoS attack) or distributed denial-of-service attack (DDoS attack) is an attempt to make a computer or network resource unavailable to its intended users. Generally, DoS attacks consists of the concerted efforts of a person, or multiple people to prevent a network site or service from functioning efficiently or at all, temporarily or indefinitely. Targets of DoS attacks can include sites or services hosted on high-profile web servers such as cloud computing providers, e-commerce sites, banks, credit card payment gateways, and root name servers.
One common method of attack involves saturating the target machine with external communications requests, such that it cannot respond to legitimate traffic, or responds so slowly as to be rendered effectively unavailable. Such attacks usually lead to a server overload. In general terms, DoS attacks are implemented by either forcing the targeted computer(s) to reset, or consuming its resources so that it can no longer provide its intended service or obstructing the communication media between the intended users and the victim so that they can no longer communicate adequately.